I run a full 3" system with an X-pipe and thats because I was figuring to make in the 550 to 625 hp range and I knew I would race through the full exh all the time. Honestly a 2.5 system will work fine for your setup. Myself if I planned to make close to 600 hp and I can run any size I want then I would use the 3". If tailpipe room is tight then you can run 2.5 tailpipes on a 3" system and not loose any power. I went with the 3" tailpipes also because my B-body has plenty of room as you can see and my tailpipes have not hit or never rattle at all. They fit fine on my stock B-body with no tubs and the springs in stock location. For what you are doing I would run 2.5 unless you plan to step up alot in the near future. Ron